Dynamics of particle laden plume in linearly stratified environment

Particle laden plumes, which are common in geophysical flows, were simulated experimentally and their flow dynamics was studied. Particles having mean size, $d_{p}=100 \mu m$, density, $\rho_{p}$=2500 kgm$^{-3}$, and volume fraction, $\phi_{v}$= 0-0.7$\%$, were injected along with lighter buoyant fluid into a linearly stratified medium (N=0.67 s$^{-1}$). It was observed that a particle-laden plume intruding at the neutral layer is characterized by four spreading regimes: (i) radial momentum flux balanced by the inertia force; (ii) inertia buoyancy regime; (iii) fluid-particle inertia regime, and (iv) viscous buoyancy regime. The maximum height, Z$_{m}$ for $\phi_{v}>0\%$ was observed to be consistently lower than the single-phase case. In the inertia-buoyancy regime, the radial spread, R$_{f}$, for the particle laden plume advanced in time as R$_{f} \approx t^{0:68}$ which is slower compared to the single-phase plume that propagates at R$_{f} \approx t^{0.74}$. It was observed that the jet cone angle is higher for the case of particle-laden plume owing to flaring of the plume. Due to the presence of particles, `particle fall out' effect occurs forming a parabolic cloud below the plume spreading height. With increasing $\phi_{v}$, secondary umbrella formation was also observed.